Wireless communications have seen increasing use in a variety of fields and devices. For instance, identification products such as smart cards and RIFD (Radio Frequency Identification) tags are used widely in fields such as transport (e.g., ticketing, road tolling, baggage tagging), finance (e.g., debit and credit cards, electronic purses, merchant cards), communications (e.g., SIM cards for GSM (Global System for Mobile Communications) phones), and tracking (e.g., access control, inventory management, asset tracking) Many such applications involve products compliant with international standard ISO14443A identification cards, and provide RF (Radio Frequency) communication technology for transmitting data between a card or tag and a reader device. For example, in electronic ticketing for public transport, travelers can wave a card over a reader at turnstiles or other entry points, facilitating convenience and speed in the ticketing process.
Another type of wireless communication involves near-field communications (NFC), which is a type of contactless communications (e.g., for identification and networking technologies) that involves short-range wireless technology. Such applications often involve communication distances of a few centimeters, and have been used for secure communications between various devices without necessarily involving user configuration. In order to make two devices communicate, users bring them close together or even make them touch. The devices' NFC interfaces connect and configure themselves to form a peer-to-peer network. NFC can also bootstrap other wireless communication protocols, such as by exchanging the configuration and session data.
NFC communication devices can communicate using passive load-modulation (PLM) to communicate between a Tag/SmartCard Emulation (proximity integrated circuit card (PICC)) and a Reader/Writer (proximity coupling device (PCD)) by using a switch to vary antenna load, which is sensed by PCD. In instances where the PICC-side antenna is small, PLM may not be strong enough for the PCD to receive communications, and/or may not meet International Organization for Standardization (ISO) requirements. NFC communication devices can communicate using active load modulation (ALM) where there is active transmission of a signal back to the PCD from the PICC. While transmitting, the PICC can lose synchronization with the PCD field because the active modulation signal overwrites the PICC.
While wireless communications as discussed above have been useful, effecting such communication in an efficient, secure and reliable manner can be challenging. For example, data communications may be lost when a distance between devices is too great, or when communicated data becomes corrupt. These and other matters have presented challenges to different types of communications, for a variety of applications.